This invention relates to inkjet printheads, and more particularly to techniques for addressing internal contamination problems in printheads.
Inkjet pens include a printhead comprising a plurality of orifices from which ink is expelled toward a print medium such as paper. Some pens include a reservoir of ink; others are connected to an ink supply through a fluid interconnect. A plurality of ink passageways exist between the ink reservoir and a plurality of firing chambers. Each such firing chamber includes a resistive heating element which is energized upon demand to expel an ink droplet through a nozzle orifice associated with that resistive heating element. The orifices are located on a surface such that the expulsion of ink droplets out of a determined number of orifices relative to a particular position of the medium results in the production of a portion of a desired character or image. Controlled positioning of the printhead and/or print medium with further expulsions of ink droplets continues the production of more pixels of the desired character or image.
The channels through which ink flows and orifices through which the ink is expelled are continually reducing in size with technology improvements. This leads to a need for improved filtering capability to prevent blockage by small particles or impurities within the ink and/or particle contaminants resident on the inside surfaces of printhead materials after manufacture. Some current inkjet pens utilize fine mesh filters to separate particle contaminants carried in the bulk ink before it reaches the firing chambers. With a move to smaller fluidic flow pathway geometries within the printhead, a reduction in the filter mesh size for filtration capability has to be balanced with overall filter area so that the filter does not inhibit inkflow during high-speed full saturation printing. Increasing filter area can cause printhead size to increase, a detriment to printer design and cost.
The next line of defense after the filter are barrier features that are meant to trap particles just before they reach the firing chamber and nozzle. Previous solutions consisted of full height barrier features that spanned from the silicon substrate up the Kapton (TM) nozzle plate like columns. These columns were often located along the edge of the die like reef islands. The recommended minimum spacing between these columns was 15 xcexcm so that channels between adjacent barrier features could be adequately cleared during the photoimaging and etching processes. In addition, the recommended minimum barrier column diameter was 20 xcexcm to provide adequate adhesion between the barrier and the substrate and to prevent shortening of the barrier columns. With tighter nozzle spacing, large barrier islands spaced close together to trap small particles prevented adequate ink flow for high throughput images.
The minimum dimension between columns and the minimum column diameter worked well to trap contaminants in printheads whose nozzle diameters were larger than the minimum column barrier spacing because particles that passed through the barrier would simply be ejected out the nozzles. However, as nozzle diameters reduced in size smaller than the recommended barrier spacings and sizes, very small particles that pass through the barrier reef islands are trapped in the firing chamber/nozzle bore.
Techniques are described for constructing filter type features capable of entrapping particle contaminants to eliminate printing defects. These designs utilize photo-imageable barrier material to fabricate various shapes and forms to reduce feature sizes. Several of these designs utilize secondary barrier material of height less than barrier materials used to fabricate ink feed channels and firing chamber walls. Another variation describes creation of a filter mesh from two layers of reduced height barrier materials.